In recent years, the mounting density of electronic components on a substrate has increased. In the mounting of electronic components, facedown mounting for bonding electronic components via metal bumps tends to be widely employed.
Facedown mounting enables connection between electronic components with low resistance. When electrodes of an electronic component are arranged at a fine pitch, metal bumps may be accurately formed on the electrodes at a fine pitch. A facedown mounting method, as illustrated in FIG. 3A to FIG. 3D, typically involves pressing bumps against each other and heating the bumps (reflow process). In this method, an electronic component 100 (FIG. 3A) having bumps 102 formed on electrodes 101 is first prepared. Next, the bumps 102 of the electronic component 100 are pressed against each other (FIG. 3B). Next, the bumps 102 are bonded together by performing heating (FIG. 3C). However, in this method, the large diameter of the bumps in the reflow process has been a hindrance to the development of narrow pitches.
In general, electronic components having substrates made of different materials, such as a Si substrate, a compound semiconductor substrate, and an organic substrate, are bonded to each other. Because of this, electronic components tend to undergo deformation, such as warping, cracking, and disconnection, due to the stress associated with a difference in thermal expansion between substrates, which leads to a demand to increase the mechanical strength of an assembly. In order to reduce the stress between these different substrates, as illustrated in FIG. 3D, there is provided a method in which the vicinity of bumps is filled with an underfill agent 103 (organic resin material) after the reflow process (see Japanese Laid-open Patent Publication No. 2006-222422). However, this method has a problem in that it is difficult to pour a material because a narrow pitch results in a small gap between the bonded parts.
As a method for solving the above-mentioned problem in filling with an underfill agent after bonding (last-in method), there is an example in which an underfill agent is applied to the chip surface before bonding (first-in method) and a bonded part is filled with the underfill agent by way of expansion of the volume of the underfill agent by foaming or the like after bonding (see Japanese Laid-open Patent Publication No. 2012-4436). However, in this method, the bumps remain spherical, which hinders the development of fine fabrication.